The present invention relates to a water-cooled direct cycle nuclear power plant, and to a method for controlling iron concentration in cooling water in order to further decrease radioactive corrosion product concentration in reactor water.
A control method of a prior art for controlling corrosion product concentration in feed water is disclosed in Japanese Patent Laid-Open No. 61-79194, where .sup.58 Co..sup.60 Co ion concentration in reactor water is controlled at low level by maintaining Fe/Ni concentration ratio in a range of 2 to 10. However, in this control method, a sufficient consideration is not paid to the case where the nickel concentration is further decreased.
In the above prior art, the control is carried out only in dependence on Fe/Ni concentration ratio in feed water. In this control method, .sup.60 Co ion concentration was frequently higher than an expected value, although .sup.58 Co ion concentration may be maintained at low level. Namely, the Fe/Ni concentration ratio is not a sufficient control index.